The present invention relates generally to invasive devices and methods for treatment of the heart, and specifically to devices and methods for controlling the heart muscle during surgery.
Heart surgery is often accompanied by the induction of cardioplegia (elective stopping of essentially all cardiac activity by injection of chemicals, selective hypothermia, mechanical stabilization, or electrical stimuli). In humans, induced global cardioplegia is nearly always practiced in conjunction with cardiopulmonary bypass.
Recently, minimally-invasive methods of cardiac surgery have been developed, in which the heart is approached through an incision made between the ribs, without sternotomy. It is sometimes preferred that, rather than inducing cardioplegia, the surgeon mechanically restrains a portion of the heart on which a surgical procedure, such as a bypass graft, is to be performed. Various tools and methods have been developed for this purpose, such as: (a) a suction cup-based stabilization platform (e.g., the Utrecht Octopus); (b) mechanical stabilization devices, such as the CTS Access Ultima System, produced by Cardiothoracic System, Cupertino, Calif.; (c) the Octopus 2 or the EndoOctopus device, both produced by Medtronic, Minneapolis, Minn.; (d) a U-shaped metal foot and other stabilizers produced by Genzyme Surgical Products, Tucker, Ga.; (e) the Octopus Suction stabilizer, produced by fedtronic GmbH, Germany; and (f) CardioVations mechanical stabilizers produced by Ethicon Endo-Surgery, Cincinnati, Ohio.
Such mechanical restraint of the heart muscle requires that substantial force, e.g., pressure or vacuum, be applied, which can cause tissue trauma; and the implements involved interfere with the surgeon""s work. This interference typically includes reducing the surgeon""s free workspace and limiting the extent of tissue stabilization, due to concerns about tissue injury. Other effects of mechanical stabilization are described in an article, xe2x80x9cThe effects of mechanical stabilization on left ventricular performance,xe2x80x9d by Burfeind et al., European Journal of Cardio-Thoracic Surgery, 14 (1998), pp. 285-289, which is incorporated herein by reference,.
PCT patent application PCT/IL97/00012, published as Wo 97/25098, to Ben-Haim et al., which is incorporated herein by reference, describes methods for modifying the force of contraction of at least a portion of a heart chamber by applying a non-excitatory electrical signal to the heart at a delay after electrical activation of the portion. The signal may be applied in combination with a pacemaker or defibrillator, which also applies an excitatory signal (i.e., pacing or defibrillation pulses) to the heart muscle.
PCT patent application PCT/IL97/00236, which is also incorporated herein by reference, describes a pacemaker that modifies cardiac output. This pacemaker applies both excitatory (pacing) and non-excitatory electrical signals to the heart. By applying non-excitatory signals of suitable strength, appropriately timed with respect to the heart""s electrical activation, the contraction of selected segments of the heart muscle can be increased or decreased.
U.S. Pat. No. 5,651,378, to Matheny et al., and an article entitled, xe2x80x9cVagus Nerve Stimulation as a Method to Temporarily Slow or Arrest the Heart,xe2x80x9d by Matheny and Shaar, Annals of Thoracic Surgery, 63 (6) Supplement (June 1997), pp. S28-29, which are both incorporated herein by reference, describe a method to stimulate the vagus nerve in order to slow or stop a patient""s heart during coronary artery bypass grafting surgery. While these methods describe electrically-stimulating the vagus nerve, their operation is, overall, substantially similar to chemical means of inducing cardioplegia, and are therefore characterized by a generally slow time constant following application and removal of the vagal nerve stimulation.
It is an object of some aspects of the present invention to provide improved methods and apparatus for regulating motion of the heart.
It is a further object of some aspects of the present invention to provide improved methods and apparatus for reducing motion of the heart during minimally-invasive and open-chest surgery.
In preferred embodiments of the present invention, an electrical cardiac stimulator allows a patient""s heart to pump blood while inhibiting motion of a segment of the heart. The stimulator comprises one or more electrodes, preferably placed at multiple sites in or on the heart, and a control unit. The control unit administers electrical signals to at least one of the electrodes in order to reduce or substantially stop motion of the segment for the duration of signal application. Termination of signal application allows the segment, as well as the heart as a whole, to resume normal motion. Preferably, the reduction in motion of the segment, as provided by the present invention, is used to enable a surgeon to perform minimally-invasive surgery or open-chest surgery, generally without inducing global cardioplegia or requiring cardiopulmonary bypass.
In some preferred embodiments of the present invention, administration of the electrical signals is accompanied by use of a stabilizer, typically a mechanical stabilizer, in conjunction with the electrical signals to further reduce motion of the segment. Similarly, for some applications, electrical signals as provided by embodiments of the present invention are used to reduce the force appliedxe2x80x94and thus the injury producedxe2x80x94by a stabilizer, while maintaining a desired level of motion reduction.
In some preferred embodiments of the present invention, one or more motion sensors, e.g., accelerometers, are coupled to the heart, and send motion signals to the control unit indicative of the segment""s motion and, optionally, of the motion of other areas of the heart. Preferably, the motion signals serve as feedback to enable the control unit to adjust the electrical signals applied to the heart, in order to reduce the detected motion of the segment. In a preferred embodiment, one of the motion sensors is coupled to the segment of the heart, adjacent to a surgical location within the segment, and is in a vicinity of at least one motion-reduction electrode. The control unit receives motion signals from the sensor, and actuates the motion-reduction electrode to apply the electrical signals, referred to herein as xe2x80x9cmotion-reduction pulses,xe2x80x9d in order to change contractility and contraction timing of muscle in the segment.
The motion-reduction pulses preferably comprise one or more of: regular pacing pulses, rapid pacing pulses, a fencing signal, and an enhancement signal. The enhancement signal is typically similar to signals used for Excitable Tissue Control, as described in U.S. Pat. application Ser. No. 09/260,369, which is assigned to the assignee of the present patent application and incorporated herein by reference. Most preferably, the motion-reduction pulses are synchronized with the overall heartbeat, and have timing, shape, and magnitude characteristics which are determined during a calibration period of the control unit. During the calibration period, a high degree of stabilization is preferably achieved, while maintaining adequate safety margins, e.g., acceptable standard patient vital signs, and avoidance of fibrillation and arrhythmia.
Generally, motion of the segment is characterized by a sum of: (a) a first component, consisting of motion resulting from general contraction and relaxation of the heart, which may depend on parameters of stimulation applied through the one or more motion-reduction electrodes and the contraction force generated thereby; and (b) a second component, consisting of local motion resulting from that part of the heart which is substantially stimulated by the motion-reduction electrodes. It is a goal of this embodiment of the present invention to apply motion-reduction pulses which alter the motion of the first and second components, particularly with respect to the timing thereof, such that the net motion of the segment, resulting from summing the two components, is generally minimized and/or smoothed.
In some of the embodiments in which a mechanical stabilizer is used in conjunction with the applied signals, the control unit typically places a greater emphasis on reducing the second component than on reducing the first component. It is believed that mechanical stabilizers are generally more successful in reducing the global component of the heart""s motion which is transferred to a local region of the heart than in reducing movements generated within the local region.
In some preferred embodiments of the present invention, the electrodes are placed at multiple sites on the epicardium and/or endocardium of the segment of the heart. Alternatively or additionally, the electrodes are placed in blood vessels of the heart or in a vicinity of the heart, and, optionally, on areas of the heart other than the segment. Typically, each electrode conveys a particular waveform to the heart, which may differ in certain aspects from the waveforms applied to other electrodes. The particular waveform to be applied to each electrode is preferably determined by the unit under the control or supervision of a human operator, in such a manner as to minimize the motion of the segment.
A U.S. patent application filed on even date, entitled, xe2x80x9cInduction of cardioplegia using applied electrical signals,xe2x80x9d which is assigned to the assignee of the present invention and is incorporated herein by reference, describes methods for applying electrical signals to the heart to induce a global cardioplegic state. Aspects of such methods may also be used in conjunction with the principles of the present patent application. In a preferred embodiment of the present invention, the electrical signals applied to the heart comprise rapid pacing pulses and/or fencing signals, as described hereinbelow, applied through one or more of the electrodes placed on or in a vicinity of the segment, in order to induce a state of generally constant and/or reduced contraction of the segment for a predetermined time period. The use of such pulses is described further in the above-mentioned application regarding induction of cardioplegia. Additionally, the signals may be applied to other regions of the heart in order to modify contraction parameters in the other regions (e.g., timing and strength), such that motion of the segment is reduced.
In some preferred embodiments of the present invention, a xe2x80x9cfencingxe2x80x9d signal is applied through one or more of the electrodes, preferably in order to prevent or inhibit the propagation of an action potential from one region of the heart to another. Fencing may be applied in conjunction with any (or none) of the motion-reduction pulses described hereinabove. Most preferably, the fencing signal is applied in a vicinity of the segment. Such fencing is described in U.S. patent application Ser. No. 09/254,903, which is assigned to the assignee of the present patent application and incorporated herein by reference. Fencing is typically used, according to these embodiments, to reduce a motion and/or a contraction force of the segment, generally by blocking or reducing the normal propagation of signals, and sometimes by applying the fencing signal to one or more sites within the segment.
In some preferred embodiments of the present invention, periods of electrical signal application are separated by signal non-application periods. Preferably, the durations of the application and non-application periods are set to maximize the surgeon""s time for performing surgery, while continuing to generally assure that the patient""s systemic oxygen needs are satisfied.
For some applications, it may be desirable to partially (and, in some cases, significantly) reduce the overall output of the heart in order to attain a high degree of stabilization of the segment for a short time. Suitable methods of electrical control of the heart to reduce cardiac output are described in the above-mentioned PCT patent applications PCT/IL97/00012 and PCT/IL97/00236, for example, and in the corresponding U.S. national phase patent applications, Ser. Nos. 09/101,723 and 09/254,900, which are assigned to the assignee of the present patent application and incorporated herein by reference. It is emphasized that in these embodiments, as in most applications of the present invention, the patient""s vital signs are preferably monitored substantially continuously.
In some preferred embodiments of the present invention, an automatic or operator-assisted feedback loop is used in order to optimize the level of stabilization, without undesirably changing measured physiological parameters, such as, for example, pCO2, pO2, Left Ventricular Pressure (LVP), ECG, and systemic blood pressure. Preferably, an abnormal value of any of these parameters triggers an alarm, responsive to which the operator and/or the control unit initiates an appropriate response. Further preferably, arrhythmia and fibrillation detection capabilities, as well as appropriate treatment protocols, are incorporated into the control unit.
Preferably, application of the electrical signals in accordance with the present invention stabilizes the segment within a very short period, typically about 1 second, and can maintain the segment""s stability for prolonged periods. The heart typically returns to normal function within about 2 seconds of removal of the electrical signals.
There is therefore provided, in accordance with a preferred embodiment of the present invention, a method for performing a medical procedure on a beating heart, including:
applying electrical signals to the heart so as to reduce motion of a segment thereof; and
performing the procedure while the heart continues to pump blood.
Preferably, applying the signals includes modifying contraction of muscle tissue of the heart, wherein modifying the contraction includes inducing contraction of the muscle tissue.
Further preferably, applying the signals includes:
determining an aspect of the motion of the segment due generally to contraction of muscle tissue outside the segment; and
adjusting the signals so as to reduce the aspect of the motion of the segment.
Preferably, applying the signals includes applying pulses at a rate greater than 5 Hz, and most preferably greater than 10 Hz.
In a preferred embodiment, the method includes mechanically stabilizing the segment in conjunction with applying the electrical signals.
Preferably, applying the electrical signals includes applying bipolar signals or, alternatively or additionally, unipolar signals.
Preferably, applying the electrical signals includes calibrating the signals intermittently during the procedure.
In a preferred embodiment, applying the electrical signals includes applying a first signal so as to precondition a response of the heart to a subsequent signal, which reduces the motion during the procedure.
Preferably, performing the procedure includes performing a treatment on the segment.
Further preferably, applying the signals includes:
intermittently applying the signals, to reduce motion of the segment; and
intermittently removing the signals, to enable the heart to pump blood regularly.
In a preferred embodiment, applying the signals includes:
sensing electrical activity of the heart to detect arrhythmia thereof; and
applying electrical energy to the heart to treat the arrhythmia.
In a preferred embodiment, the method includes performing thoracic surgery while motion of the segment is reduced.
Alternatively, the method includes performing a diagnostic procedure while motion of the segment is reduced.
Preferably, the method includes, sensing motion of the heart, wherein applying the signals includes modifying a characteristic of at least some of the signals applied to the heart responsive to the sensed motion. Most preferably, sensing the motion includes coupling at least one motion sensor to detect motion of the segment of the heart, wherein modifying the characteristic includes modifying a signal characteristic so as to reduce the motion of the segment.
In a preferred embodiment, applying the signals includes applying a fencing signal to the heart to block propagation of an activation wave into the segment of the heart. Alternatively or additionally, applying the signals includes applying a fencing signal in a vicinity of the segment to reduce a contraction force thereof.
Preferably, applying the electrical signals includes applying signals, most preferably including pacing signals, at a plurality of sites on the heart. Most preferably, applying the signals includes applying a first waveform at a first one of the sites and applying a second waveform, which differs from the first waveform, at a second one of the sites, wherein applying the first and second waveforms includes controlling a timing relationship of the waveforms so as to reduce the motion of the segment.
There is also provided, in accordance with a preferred embodiment of the present invention, apparatus for performing a medical procedure on a beating heart, including:
one or more electrodes, coupled to the heart; and
a control unit, which actuates the electrodes to apply electrical signals to the heart so as to substantially reduce motion of a segment thereof while the heart continues to pump blood, whereby the procedure is performed on the segment.
Preferably, the signals cause contraction of muscle tissue of the heart.
Preferably, the electrodes include one or more local sense electrodes, coupled to the heart and to the control unit, which sense electrical activity of the heart to detect arrhythmia thereof, and convey a signal responsive to the sensing to the control unit.
Further preferably, the apparatus includes one or more motion sensors, coupled to the heart and to the control unit, which sense motion of the heart, wherein the control unit modifies the signals applied to the heart responsive to the motion. Most preferably, at least one of the one or more motion sensors is coupled to the segment of the heart, and the control unit modifies the signals so as to minimize motion sensed by the at least one sensor.
In a preferred embodiment, the apparatus includes one or more fencing electrodes, coupled to the heart, which are actuated by the control unit to apply a fencing signal to the heart so as to block propagation of an activation wave into the segment. Alternatively or additionally, the one or more fencing electrodes are actuated by the control unit to apply a fencing signal to the segment so as to reduce a contraction force thereof.
In another preferred embodiment, the apparatus includes a mechanical stabilizer, which is applied to the heart to restrain motion thereof, in conjunction with motion reduction using the one or more electrodes.
There is further provided, in accordance with a preferred embodiment of the present invention, a method for performing a medical procedure on muscle tissue having a tendency to motion, including:
applying electrical signals to the tissue so as to reduce motion of a segment thereof, such that the motion increases spontaneously upon removal of the signals; and
performing the procedure while the motion is reduced.
Preferably, the muscle tissue includes heart tissue or, alternatively or additionally, smooth muscle or skeletal muscle.
Preferably, performing the procedure includes performing a diagnostic procedure or, alternatively or additionally, a therapeutic procedure.
There is moreover provided, in accordance with a preferred embodiment of the present invention, apparatus for performing a medical procedure on muscle tissue having a tendency to motion, including:
one or more electrodes, coupled to the tissue; and
a control unit, which actuates the electrodes to apply electrical signals to the tissue so as to reduce motion of a segment thereof, whereby the procedure is performed on the segment, and such that the motion increases spontaneously upon removal of the signals.
The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings, in which: